1. Field of the Invention
This invention relates to improved production of gas, particularly methane, by accelerated bioleaching of organic materials, such as from sanitary landfills or other confined deposits of organic matter.
2. Description of the Prior Art
Methane producing anaerobic digestion is well known and two-phase anaerobic digestion is known to the art and further disclosed in U.S. Pat. No. 4,022,665. Methane production by anaerobic digestion of garbage utilizing a liquor from anaerobic sewage sludge digestion is taught by U.S. Pat. No. 2,572,767.
Sanitary landfills formed by filling a land area with successive layers of solid waste, principally household waste, and layers of earth or soil are well known. The uncontrolled landfill depends upon natural biological action, precipitation and climate to effect decomposition. In areas where oxygen is present, the decomposition will be aerobic and in areas where little oxygen is present, such as at the deeper depths, decomposition will be slower and anaerobic producing methane containing gas. Initially, there is no methane production from the landfill and it increases very slowly with time to an amount representing only about 15 to 20 percent of the total potential production after many years. The formed methane is an explosion or fire hazard and may migrate to buildings or structures several hundred feet from the landfill if not removed from the landfill. Further, the natural precipitation draining out of the landfill may carry highly toxic contaminated water to contaminate underground water supplies, surface streams and wells. Due to the very slow stabilization, the uncontrolled landfill is not usable for other purposes for long periods of time and thus, particularly near metropolitan areas, represents a large waste of land resources.
One approach to rendering waste disposal landfills safer is suggested by U.S. Pat. No. 3,586,624 which teaches a liquid impervious containment of the lower portion of the landfill with continuous flow of water through the landfill to accelerate the decomposition, decrease the fire hazard and flush contaminants from the landfill in a controlled manner. The water drained from the landfill may be treated for removal of contaminants and recycled to the landfill. The combination of refuse with earth and industrial liquid wastes such as asphalts with earth to avoid liquid movement are taught by U.S. Pat. Nos. 3,705,851 and 3,732,697, respectively.
In the past, methane gas has been frequently vented and flared from concentrations of organic wastes, such as landfills, as a safety precaution. However, in recent years and especially in view of energy conservation, the recovery and utilization of methane from sanitary landfills and desirability of early utilization of the landfill area for other purposes has been recognized. "Methane Production, Recovery, and Utilization from Landfills," James, S. C. and Rhyne, C. W., Symposium Papers on Energy from Biomass and Wastes, Washington, D.C., Aug. 14-18, 1978, pgs. 317-324, and "Recovery and Utilization of Methane Gas from a Sanitary Landfill--City of Industry, Calif., " Stearns, R. P., Wright, T. D. and Brecher, M., Symposium Papers on Energy from Biomass and Wastes, Washington, D.C., Aug. 14-18, 1978, pgs. 325-343. Presently methane is most frequently recovered from landfills by pipes extending into the landfill and transporting the methane containing gas formed within the landfill to a collecting area for further treatment.
In the United States, about 1151 million tons (dry) of organic wastes are generated annually in the form of municipal solid waste, agricultural residue, manure, logging and wood manufacturing residues, municipal sludge solids, industrial organic wastes and miscellaneous organic wastes representing production potential of 11.8 trillion SCF/yr. of substitute natural gas (SNG). The most readily available solid waste for energy recovery is municipal solid waste estimated to be currently generated at about 260 million tons per year in the United States. Additionally, urban areas in the United States produce about 25 million tons (dry) per year of organic waste solids in sewage sludge. These wastes have presented intractable waste management and disposal problems and represent continuing loss of energy resources.